The invention relates to a method for producing a catalytic converter.
In connection with the manufacture of catalytic converters with ceramic monolith substrates, it is necessary to protect the monolith in the catalytic converter housing from mechanical stress. This is generally accomplished using an expanded or intumescent mat, which cushions the monolith from the metallic catalytic converter housing.
Catalytic converter housings such as those used to secure a catalyst in the exhaust systems of internal combustion engines, more particularly those of motor vehicles, exist in a variety of embodiments, wherein two systems have prevailed in the market. In the first system, a monolith (usually made of ceramic), coated with a catalytically active material, is wrapped in an intumescent mat that supports the monolith. Together with the monolith, this intumescent mat is then placed in a pre-rolled sheet-metal jacket which holds the monolith and the intumescent mat in position. The pretensioned sheet-metal jacket is subsequently tacked at individual points by means of spot welding. Inlet and outlet cones for connection to an exhaust pipe are affixed to the end faces of the jacket. The cones are attached by a continuous circumferential weld seam on the wound converter. The sheet-metal jacket is then closed by a weld seam yielding the finished catalytic converter.
The manufacture of a catalytic converter housing by means of a winding and tensioning technique of this type, such as is described in EP 0 818 615 A2, for example, has basically proven itself, but is capable of improvement with regard to secure retention of the monolith inside the housing jacket by means of the intumescent mat.
A second system in the market is known as a clamshell converter, and consists of a monolith, a separate intumescent mat and two shell halves, specifically a top shell half and a bottom shell half. However, process reliability is often inadequate in the case of clamshell converters. Moreover, the geometry determined by the shell shape frequently causes difficulties in adapting to motor vehicle underbodies.
The object of the invention is to provide a method for manufacturing a catalytic converter with a housing using the winding and tensioning technique, wherein the catalytic converter core, particularly a monolith, can be retained in an especially secure and permanent manner within the housing jacket, thereby ensuring long-term stability of the catalytic converter over its lifetime.